Reusable polymer-supported amine-copper catalyst for the formation of α-alkylidene cyclic carbonates in supercritical carbon dioxide

Article abstract of DOI:10.1002/ejoc.200701165

A green, simple and effective polymer-supported catalytic system has been developed for the cyclization of propargyl alcohols with carbon dioxide (CO ₂). α-Alkylidene cyclic carbonates were obtained in satisfactory isolated yields in most cases. The catalyst could be recovered by simple filtration and reused several times without significant loss of activity. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200701165

FULL PAPER
DOI: 10.1002/ejoc.200701165
Reusable Polymer-Supported Amine-Copper Catalyst for the Formation of
α-Alkylidene Cyclic Carbonates in Supercritical Carbon Dioxide
Huan-Feng Jiang,*[a] A-Zhong Wang,[a] Hai-Ling Liu,[a] and Chao-Rong Qi[a]
Keywords: Polymer-supported catalysts / Carbon dioxide fixation / Cyclic carbonates / Supercritical carbon dioxide /
Cyclization / Copper
A green, simple and effective polymer-supported catalytic
system has been developed for the cyclization of propargyl
cases. The catalyst could be recovered by simple filtration
and reused several times without significant loss of activity.
alcohols with carbon dioxide (CO2). α-Alkylidene cyclic car- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
bonates were obtained in satisfactory isolated yields in most
Germany, 2008)
(dimethylamino)methyl-polystyrene-supported
copper(I)
Introduction
iodide (DMAM-PS-CuI) as an efficient and environmen-
tally benign heterogeneous catalyst for the cyclization of
CO2 and propargyl alcohols under supercritical conditions
(Scheme 1).
CO2 is an environmentally benign and abundant C1 re-
source, and therefore considerable attention has been fo-
cused on the fixation of carbon dioxide (CO2) to organic
substrates.[1] The formation of α-alkylidene cyclic carbon-
ates from CO2 and propargylic alcohol is an attractive route
for the chemical fixation of CO2 because α-alkylidene cyclic
carbonates are useful building blocks in organic synthesis.[2]
It has been reported that transition metals, including Cu,[3]
Co,[4] Ru,[5] Pd[6] and Ag,[7] or tertiary phosphanes[8] are
effective catalysts for the preparation of α-alkylidene cyclic
carbonates. However, in most cases, the reactions have been
accomplished under homogeneous catalytic conditions.
Therefore, it is still desirable to search for a highly efficient,
easily separating and recyclable catalytic system for this
transformation.
Scheme 1. Carboxylative cyclization of propargyl alcohols with
scCO2 catalyzed by DMAM-PS-CuI.
Results and Discussion
Reviewing the developments in transition-metal-cata-
lyzed reactions of CO2 and propargylic alcohols,[3–7] we
found that the desired cyclic carbonates were obtained in
the presence of a stoichiometric amount of base. Amine
resin, as a dual-purpose polymer-supported organic base
and transition-metal ligand, is easily separated and reco-
vered from the reaction mixture. Thus, we surmised that
amine-resin-supported copper(I) iodide might be employed
as an effective and reusable catalyst for the fixation reac-
tion. On the other hand, the use of supercritical carbon
dioxide (scCO2) as a reactant and promising reaction me-
dium has recently received much attention, not only be-
cause of its benign character, but also because of its greater
activity and selectivity.[9,10] In this paper, we report on
The reaction of 2-methylbut-3-yn-2-ol (1a) with CO2 was
chosen as the model reaction to test the catalytic capability
of DMAM-PS-CuI, and the results are summarized in
Table 1. Initially, the amount of DMAM-PS-CuI was varied
under 14 MPa of CO2 at 40 °C; the results showed that an
increase in the amount of catalyst enhanced the reaction
yields (Table 1, Entries 1–4). Without any catalyst, this reac-
tion did not take place even after 24 h (Table 1, Entry 1),
whereas 48% yield (by GC) of 2a was obtained when 3 mol-
% of DMAM-PS-CuI was added (Table 1, Entry 2). By fur-
ther increasing the amount of DMAM-PS-CuI to 8 mol-%,
the yield of 2a sharply increased to 99% (Table 1, Entry 4).
Then the effect of the reaction pressure was examined; the
results indicated that the pressure strongly influenced the
carboxylative cyclization. When the pressure was increased
from 14 to 18 MPa, the yield of 2a slightly decreased
(Table 1, Entries 4–6). However, reducing the pressure from
10 to 6 MPa had an obvious impact on the yield of 2a
(Table 1, Entries 9–11). The most suitable CO2 pressure
ranges from 12 to 16 MPa (Table 1, Entries 4, 7 and 8). The
[a] The College of Chemistry, South China University of Tech-
nology,
Guangzhou 510640, P. R. China
Fax: +86-020-87112906
E-mail: jianghf@scut.edu.cn
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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H.-F. Jiang, A.-Z. Wang, H.-L. Liu, C.-R. Qi
FULL PAPER
effect of temperature was also evaluated. The reactions at difficult to manipulate and recover compared with the
both 40 and 60 °C gave satisfactory results (Table 1, En- heterogeneous catalyst.
tries 10 and 12). When the temperature was reduced to 30
Table 1 also shows the reusability of the supported cata-
or 25 °C, only small quantities of the desired product were lyst (Entries 21–24). DMAM-PS-CuI could be recovered
obtained (Table 1, Entries 13 and 14). A yield of 77% was easily by simple filtration and reused after minimal treat-
obtained with CuI alone as the catalyst and Et3N (10 mol- ment. The results showed that the reused DMAM-PS-CuI
%) as base (Table 1, Entry 15). This result thus shows that still retained its catalytic activity after multiple trials, but its
the CuI catalytic activity is significantly enhanced by fixing catalytic capacity decreased with increasing reuse. To exam-
it to the polymer-supported base. We examined the ability ine whether some leaching of Cu occurred during the reac-
of several other metal salts to activate the propargyl alcohol tion, the filtrate obtained after filtration was analyzed by
[7]
under a CO2 pressure of 12 MPa. CuCl[3] and AgBF4 af- ICP-AES which showed the amount of Cu present in the
forded the cyclic carbonate in 73 and 81% yields, respec- filtrate was less than 0.3% of the initial amount. For com-
tively (Table 1, Entries 16 and 17), [Ru3(CO)12][5] showed lit- parison with DMAM-PS-CuI, the cyclization of 1a was
tle activity towards this reaction (Table 1, Entry 18), and performed with 8 mol-% of CuI and 24 mol-% of DMAM-
[Pd(OAc)2][6] produced only a trace amount of the cyclic PS; the product was obtained in only 48% yield (Table 1,
carbonate (Table 1, Entry 19).
Entry 25). It is suspected that physical destruction of the
polymer matrix by stirring and leaching of Cu might be
responsible for this decline.
Table 1. Formation of 4,4-dimethyl-5-methylene-1,3-dioxolan-2-
one (2a) from the reaction of 2-methylbut-3-yn-2-ol (1a) with
CO2.[a]
Under the optimized reaction conditions, other propar-
gyl alcohols 1a–1k were allowed to react with CO2 and af-
forded the corresponding products in good to high yields.
When tertiary propargyl alcohols 1b–1f were employed, the
aliphatic-substituted alcohols, whether 3,4-dimethyl-1-pen-
tyn-3-ol, 3-methylnonyn-3-ol or five- or six-membered-ring-
substituted propargyl alcohols, afforded the corresponding
cyclic carbonates in good to excellent yields (Table 2, En-
tries 1–4). When the aliphatic substituent was replaced with
an aromatic group such as phenyl, unfortunately, the de-
sired product was not observed under the same conditions,
and a large amount of unreacted starting material was reco-
vered (Table 2, Entry 5). Note that secondary propargylic
alcohols 1g–1j gave the corresponding cyclic carbonate
products 2g–2j in high yields (Table 2, Entries 6–9). When
primary and internal propargylic alcohols were used as the
substrates, the desired products were not detected (Table 2,
Entries 10 and 11), which suggests that the present method-
ology could be specific to aliphatic-substituted secondary
and tertiary terminal propargylic alcohols.
Entry Catalyst
Pressure Temp.
Yield
[%][b]
[MPa]
[°C]
1
2
3
4
5
6
7
8
–
14
14
14
14
16
18
13
12
10
8
40
40
40
40
40
40
40
40
40
40
40
60
30
25
40
40
40
40
40
40
40
40
40
40
40
0
DMAM-PS-CuI (3 mol-%)
DMAM-PS-CuI (5 mol-%)
DMAM-PS-CuI (8 mol-%)
DMAM-PS-CuI (8 mol-%)
DMAM-PS-CuI (8 mol-%)
DMAM-PS-CuI (8 mol-%)
DMAM-PS-CuI (8 mol-%)
DMAM-PS-CuI (8 mol-%)
DMAM-PS-CuI (8 mol-%)
DMAM-PS-CuI (8 mol-%)
DMAM-PS-CuI (8 mol-%)
DMAM-PS-CuI (8 mol-%)
DMAM-PS-CuI (8 mol-%)
CuI (8 mol-%)
48
77
99
98
96
99
99
97
84
53
99
46
22
77
73
81
46
9
10
11
12
13
14
15[c]
16[c]
17[d]
18[c]
19[c]
20
21
22
23
24
25[e]
6
12
12
12
12
12
12
12
12
12
12
12
12
12
12
A plausible mechanism for the incorporation of CO2 into
propargylic alcohols is postulated in Scheme 2, and it is
similar to the mechanism reported previously for other cat-
CuCl (8 mol-%)
AgBF4 (8 mol-%)
[Ru3(CO)12] (8 mol-%)
[Pd(OAc)2] (8 mol-%)
P(n-C4H9)3 (8 mol-%)
DMAM-PS-CuI (2nd)
DMAM-PS-CuI (3rd)
DMAM-PS-CuI (4th)
DMAM-PS-CuI (5th)
CuI (8 mol-%)
trace
95
96
91
84
78
48
[a] Reaction conditions: 2-methylbut-3-yn-2-ol (1a) (1 mmol),
DMAM-PS-CuI (1.21 mmol of CuI/g; 24.8 mg, 0.03 mmol CuI,
3 mol-%; 41.3 mg, 5 mol-%; 66 mg, 8 mol-%), 24 h. [b] Determined
by GC. [c] Et3N (24 mol-%) as base. [d] DBU (24 mol-%) as base.
[e] DMAM-PS (50.5 mg, 4.8 mmol N/g, 24 mol-%) as base.
[8]
P(n-C4H9)3 exhibited a comparable activity to that of
the polymer-supported catalyst under the same reaction
Scheme 2. Proposed mechanism for CO2 incorporation into pro-
conditions (Table 1, Entry 20), but P(n-C4H9)3 tends to be pargylic alcohols catalyzed by DMAM-PS-CuI.
2310 Eur. J. Org. Chem. 2008, 2309–2312
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Formation of α-Alkylidene Cyclic Carbonates in Supercritical Carbon Dioxide
Table 2. Carboxylative cyclization of propargyl alcohols with
Conclusion
scCO2.[a]
We have presented in this paper the cyclization of pro-
pargyl alcohols with CO2 to α-alkylidene cyclic carbonates
promoted by a polymer-supported catalyst containing cu-
prous iodide and amine functions under supercritical condi-
tions. A tremendous advantage of using a polymer-sup-
ported catalyst for this transformation is that it can be eas-
ily recovered and reused after the reaction. The product can
be separated easily from the system and continuous reac-
tions might be achieved.
Experimental Section
General: NMR spectra were recorded with a Bruker DRX-400
spectrometer using CDCl3 as solvent and TMS as the internal stan-
dard. GC analyses were performed with a GC-930 chromatograph
(Shanghai Haixian Chromatograph Instrument Ltd. Co.). Mass
spectra were recorded with a Shimadzu GCMS-QP5050A spec-
trometer. Elemental analyses were performed with a Vario EL Ele-
mental Analyzer.
Materials: CO2 was supplied by Guangzhou Gases Factory CO.,
Ltd. with a purity of 99.9%. The propargyl alcohols were pur-
chased from Acros Organics and used without further purification.
CuI was purchased from Aldrich Chemical Co. Resin (DMAM-
PS) was obtained from Tianjin SHENTAI Chemical Industry Co.,
Ltd. The (dimethylamino)methyl-polystyrene-supported copper(I)
iodide (DMAM-PS-CuI) was prepared according to procedures re-
ported in the literature which gave the polymer a loading of
1.21 mmol CuI/g.[11]
Typical Experimental Procedure for the DMAM-PS-CuI-Catalyzed
Reaction of CO2 and Propargyl Alcohols: The reaction was carried
out in an HF-15 autoclave. DMAM-PS-CuI (66 mg, 1.21 mmol of
CuI/g, 0.08 mmol of CuI, 8 mol-%) and the propargyl alcohol
(1 mmol) were added to the 15-mL autoclave in sequence. Liquid
CO2 was pumped into the autoclave by a cooling pump until the
desired pressure was reached, and then the autoclave was heated
by an oil bath under magnetic stirring for 24 h. After the reaction
was finished, the autoclave was cooled to 0 °C. CO2 was vented,
and the residue was extracted with diethyl ether (10 mL). The resin
was filtered, washed with CH2Cl2 (3ϫ15 mL) and dried in vacuo
at 40 °C. The collected filtrate was concentrated under reduced
pressure. The product was purified by chromatography on a silica
gel column using light petroleum ether/ethyl acetate as eluent.
4,4-Dimethyl-5-methylene-1,3-dioxolan-2-one (2a):[8d] 1H NMR
(CDCl3, 400 MHz): δ = 1.59 (s, 6 H), 4.29 (d, J = 4.0 Hz, 1 H),
4.75 (d, J = 3.6 Hz, 1 H) ppm. 13C NMR (CDCl3, 100 MHz): δ =
27.5, 84.6, 85.2, 151.2, 158.6 ppm. MS (EI, 70 eV): m/z (%) = 128
(4) [M]+, 84 (46), 69 (22), 56 (96), 41 (100).
[a] Reaction conditions: propargyl alcohols (1 mmol), 66 mg of
resin (1.21 mmol of CuI/g, 0.08 mmol of CuI, 8 mol-%), 14 MPa,
40 °C, 24 h. [b] Determined by GC. [c] Isolated yield.
Supporting Information (see also the footnote on the first page of
this article): Experimental procedures and analytical and spectral
characterization data for all compounds.
alysts.[4,7] The first step of the reaction is the formation of
carbonate intermediate A from 1 and CO2 activated by the
amine group of DMAM-PS-CuI. Then the intermediate A
undergoes cyclization with the assistance of CuI to afford
the corresponding cyclic carbonate and the release of the
polymer-supported catalyst.
Acknowledgments
The authors thank the National Natural Science Foundation of
China (Nos. 20772034, 20625205, 20572027 and 20332030) and the
Guangdong Natural Science Foundation (No. 07118070) for their
financial support of this work.
Eur. J. Org. Chem. 2008, 2309–2312
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FULL PAPER
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Received: December 8, 2007
Published Online: March 19, 2008
2312
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